Mercury is an incredibly stubborn toxin. Once it is emitted from the smokestacks of coal-fired power plants, among other sources, the gas can drift through the atmosphere for up to a year before settling into oceans and lakes. It can then accumulate in fish as toxic methylmercury, and eventually harm the people who consume the fish. What's more, mercury that was previously emitted can actually re-enter the atmosphere through evaporation. Read more...